Method of fabricating preoxidizbd silver-cadmium
oxide electrical contacts

ABSTRACT

A METHOD OF MANUFACTURING PREOXIDIZED SILVER-CADMIUM OXIDE MATERIALS COMPRISING, ATOMIZING MOLTEN SILVER-CADMIUM ALLOY TO FORM SILVER-CADMIUM ALLOY PARTICLES, COOLING SAID PARTICLES, INTERNALLY OXIDIZING CADMIUM CONTAINED IN THE PARTICLES, COMPACTING AND HEATING THE OXIDIZED PARTICLES, EXTRUDING THE COMPACTED PARTICLES TO FOR A DESIRED SHAPE AND WORKING THE SHAPE TO THE EXTENT NECESSARY TO OBTAIN THE DESIRED FINAL SIZE.

Feb. 23, 1971 P c. MURPHY ETAL Re. 27,075

METHOD OF FABRfCATING PREOXIDIZED SILVERGADMIUM 3 Sheets-Sheet 1 OXIDE ELECTRICAL CONTACTS Original Filed April 2, 1965 INVEN TOR FRED/WK 0. H44 RBYE ATTORNEY Feb. 23, 1971 METHOD OF FABRICATING PREOXIDIZED SILVER OXIDE ELECTRICAL CONTACTS 1965 5 Sheets-Sheet 2 Original Filed April 2,

EFFECT OF SHOTTI NG METHOD ON SHOT SIZE MAXIMUM DESIRABLE SHOT SIZE FOR MANUFACTURE OF STRIP ;}TAETALL I2 I -55 sun JET

, AIR 8. WATER (MAXIMUM DESIRABLE SHOT SIZE FOR MANUFACTURE OF WIRE AIR JET/\\\ Y .L ELL -/CYCLONE 0 o O 0 0 0 0 O O 0 9 8 7 6 5 4 3 2 l IOO PARTICLE MESH SIZE FIQZ 4 L PROPERTIES OF PRE-OXIDIZED MATERIAL O w z m TENS! LE STRENGTH ANNEALING TEMPERATURE C INVENTOR BY FREDR/K 0. HAARBYE ATTORNEY TENSILE STRENGTH PSI X I000 Feb. 23, 1971 p. C MURPHY ETAL Re. 27,075

METHOD OF FABRICATING PREOXIDIZED SILVER-CADMlUM OXIDE ELECTRICAL CONTACTS Original Filed April 2, 1965 3 Sheets-Sheet 3 EFFECT OF co o WORK ON PHYSICAL PROPERTIES OF PRE-OXIDIZED MATERIAL so 1 g m .7 ..V V V V A TENSILE STRENGTH j /(H/:RDNESS w 7 V V V 7-- if V E g I 89 Z 8 I a w y .W E .7 .Hw .EE/- E mum UV V E V .E E M 2 as g z I ;0NDUCTIVITY E as 0 U) E U D N 2 O E C r 5 U 5 as g '0 ELONGATION I d a5 2 5 0 {5 IO 20 3o 40 so so 0.

AMOUNT OF COLD WORK- PERCENT REDUCTION BY AREA FIG 6 INVENTOR FRED/WK O. HAARBYE BY/gdjz ATTORNEY United States Patent i p 27,075 METHOD OF FABRICATING PREOXIDIZED SILVER-CADMIUM OXIDE ELECTRICAL CONTACTS Peter C. Murphy and Fredrik O. Haarbye, Indianapolis, Ind.; said Haarbye assignor to P.R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Original No. 3,317,991, dated May 9, 1967, Ser. No. 445,038, Apr. 2', 1965. Application for reissue May 8, 1969, Ser. No. 830,898

Int. Cl. 1322f 3/24 US. Cl. 29-4205 17 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE A method of manufacturing preoxidized silver-cadmium oxide materials comprising, atomizing molten silver-cadmium alloy to form silver-cadmium alloy particles, cooling said particles, internally oxidizing cadmium contained in the particles, compacting and heating the oxidized particles, extruding the compacted particles to form a desired shape and working the shape to the extent necessary to obtain the desired final size.

The present invention relates generally to the fabrication of wire and strip materal and more particularly relates to means and methods for the fabrication of preoxidized silver-cadmium oxide materials for use in electrical contacts.

Preoxidized silver-cadmium oxide Wire and strip may be fabricated by any one of the following three basically different procedures:

(a) Manufacture from silver and cadmium oxide powders.

(b) Manufacture from internally oxidized silvercadmium shot or grain.

(c) Manufacture by internally oxidizing silver-cadmium wire or strip prior to manufacture of the final part.

The manufacture of silver-cadmium oxide wire from silver and cadmium oxide powders is expensive due to the high powder cost and very limited workability. Several attempts have been made to oxidize silver-cadmium alloy wire. However, no practical method has yet been devised for production of wire with the required ductility. Although preoxidized wire has become available within the last several years, it is only recently that the wire quality has been satisfactory for general heading applications.

The present invention discloses a unique method for the manufacture of preoxidized wire and strip comprising the steps of casting the silver-cadmium shot, internally oxidizing said shot, compacting the oxidized shot, extruding the compacted shot, and cold working the extruded shape to fiinal size.

It is an object of the present invention, therefore, to provide a superior method of fabricating electrical contact material wherein silver-cadmium shot is internally oxidized.

It is another object of the present invention to disclose a manufacturing method which is economically superior to the use of silver and cadmium oxide powders because of the lower cost of the base materials.

Still another object of the present invention is to disclose a manufacturing method which is superior to the use of silver and cadmium oxide powders because, of

Re. 27,075 Reissued Feb. 23, 1971 higher density, better conductivity, and greater workability in the finished material.

Yet another object of the present invention is to disclose a method of manufacturing preoxidized silvercadmium oxide materials which is superior to the use of post-oxidized materials because of shorter fabrication time, harder contact surfaces, less scrap of the expensive formed contact part, and better dimensional control of the finished part.

Still another object of the present invention is to disclose a method of manufacturing pr eoxidized silvercadmium oxide materials which avoids a center core of unoxidized material or a cadmium depleted center core and requires no sorting of the contact parts due to oxidation defects.

The present invention, in another of its aspects, relates to novel features of the instrumentali'ties described herein for teaching the principal object of the invention and to the novel principles employed in the instrumentalities whether or not these features and principles may be used in the said object and/or in the said field.

Other objects of the invention and the nature thereof will become apparent from the following desrciption considered in conjunction with the accompanying drawings and wherein like reference numbers describe elements of similar function therein [and wherein the scope of the invention is determined rather from the dependent claims].

For illustrative purposes, the invention will be described in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of the casting assembly construction.

FIG. [3] 2 is a top view of the funnel;

FIG. [2] 3 is a sectional view of the funnel;

FIG 4 is a graph showing the effect of the shotting method on shot size;

FIG. 5 is a graph indicating the recovery rate of' a completely soft condition is very slow; and

FIG. 6 is a graph showing the effect of cold work on preoxidized material and on the same material prior to oxidation.

Referring now to the process encompassed by the present invention, the first step under consideration is the casting of silver-cadmium shot.

7 Disintegration of molten metal has long been a convenient technique for producing small metal particles or shot. Numerous patents have disclosed methods for atomization of a molten metal stream ejected from an orifice with the use of jets of different media to aid in breaking up the stream. The factors determining the breaking-up process of the molten stream are quite complicated. After the liquid stream breaks up into fragments through friction and resistance to the atmosphere, these fragments tend to contract to droplet form due to the surface tensionof the metal. The size of the drop is largely dependent upon the size of the liquid stream and the viscosity of the molten metal.

Fine silver readily lendsitself to fragmentation into small particles by shotting. However, the addition of cadmium to the silver drastically changes the surface tension of the liquid alloy to the point where [single] simple shottin'g is not feasible. Although several approaches are available in the shotting operation for silver-cadmium alloys, the most desirable one for the present invention employs the atomization of a liquid silver-cadmium metal stream using a direct air or airwater nozzle. Ihe shotting device consists of three general parts: the funnel establishing the size of the molten metal stream, the nozzle producing the jet which breaks up the liquid metal stream into small fragments, and acollector to contain the shot or grain.

The most practical construction arrived at for the shotting funnel is illustrated in FIGS. land 3. Funnel 10 consists of a cast iron cone 11 with a graphite insert 12. Liquid m'etal prepared according to the standard melting procedure and superheated to a temperature of 1260 C. in crucible 13 is, poured into funnel 11. Crucible 13 is pivotally mounted in bracket 14 to facilitate pouring. In order to shorten the pour time and prevent excessive cooling of the molten metal .during the shotting operation, one or more holes 15 are drilled in the center of graphite insert 12, thus forming one or more metal streams 16, each having a diameter of approximately 0.095 inch. The molten streams 16 emerging from funnel 10 are subjected to a jet 17 of air or an air-water mixture. Shop air and water at regular pressures are employed and are introduced from inlets 18 and 19 respectively. The disintegrated streams 20 fan out from nozzle 21, and the metal shot 22 is collected and cooled in a metal drum 23 containing water. Drum 23 has an inner drum 24 for the actual collection of the shot. After cooling, the cooling water is drained from the shot and the shot is allowed to air dry. When completely dry the shot is screened through a No. 6 mesh screen in the case of wire, or a A inch screen for strip applications.

The next step in the process of the present invention comprises internal oxidation of the silver-cadmium shot. The dried and screened shot is loaded in shallow Inconel trays perforated on the bottom with .064 inch diameter holes for air circulation, Loading depth of the grain is approximately /2 inch. Each tray holds approximately 150 troy ounces, and a typical oxidizing furnace can accommodate 16 trays, or a total charge of 2400 troy ounces.

Oxidation is carried out at the standard oxidizing temperature for silver-cadmium oxide material, [size] such as 825 C. The furnacing cycle in air is 24 hours. In an oxygen-enriched atmosphere, i.e., by introducing oxygen into the furnace at the rate 'of 50 cubic feet per hour, the furnacing cycle is reduced to hours. Cleaning of the oxidized shot is normally not necessary unless an excessive amount of cadmium oxide is present on the surface of the shot. If cleaning is needed, a 5-minute rinse in 5% solution of H 80 followed by a thorough rinse in clean water, is recommended.

The third step in the instant process comprises the compacting of the oxidized silver-cadmium shot. The grain may be prepared for extrusion by one of the following three methods:

(a) Compacting the shot in the extrusion press container immediately prior to the extrusion.

(b) Compacting the shot into billet form by hydrostatic pressing.

(c) Compacting the shot into billet form by mechanical pressing.

In the fourth step herein, the compacted grain or shot isextruded. Immediately prior to extrusion, the compacted grain is pre-heated to a temperature of 1450 F. Air is used as the furnace atmosphere. Due to the high strength of the preoxidized material, an effective extrusion pressure of approximately 80 tons per sq. in. is required, and the billets are reverse extruded.

The fifth and final step of the present invention involves cold working the extruded shape to final size. This can be accomplished by conventional techniques.

The manufacture of preoxidized material from a disintegrated silver-cadmium alloy having the necessary formability requires a close control of each step through out the entire process.

It has been established that the maximum shot particle size desirable for the manufacture of wire is approximately 0.l32 in. or a particle size which will pass through a No. 6 mesh screen. When larger shot sizes are used, a pronounced woody structure is obtained. FIG. 4'

shows the effect of the shotting methods on shot sizes. The shotting arrangement as shown in FIG. 1 (l) minimizes the problems associated with a too rapid cooling of the liquid metal prior to passing through the small orifice; (2) prevents the flux from entering the funnel orifice and contaminating the shot; (3) increases the ease of cleaning the funnel after pour is finished; (4) prevents agglomeration by welding of the hot shot in the collector; and (5) provides for ease of removal of the shot from the collector.

The importance of preventing flux or contamination from being mixed in with the shot cannot be overemphasized. Any foreign material mixed in with the shot will seriously impede both the drawability as well as the headability of the material.

Drying of the shot is best accomplished at room temperature and spread out in a layer of about one inch thick on paper having good absorption characteristics. This minimizes the impurities transferred onto the shot from salts dissolved in the water.

Although diffusion furnaces used for batch diffusion of headed contact rivets are satisfactory for oxidation of shot, a slight stirring action is desirable to prevent formation of surface cadmium oxide by providing easy access of the furnace atmosphere to the entire shot mass, and to prevent fusion of the shot during oxidation.

FIG. 5 indicates that the recovery rate of a completely soft condition upon annealing is very slow, and is not complete at a temperature below 700 C.

FIG. 6 shows that the effect of cold work on preoxidized material (solid line) is not as pronounced as the effect of cold work on the same material (dotted line) prior to oxidation. However, the dispersion of fine particles of cadmium oxide throughout the silver matrix of preoxidized material considerably increases the strength of the material in the soft condition as compared with the original silver-cadmium materiaL'Due to the small amount of cold work desirable between anneals, the extruded size should be as close to the final size as possible.

The present invention as hereinabove described and in its representative embodiment is merely illustrative and not exhaustive in scope. Since many widely differing embodiments of the invention may be made without departing from the scope thereof, it is intended that all matters contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, we claim:

I 1. The method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized;

( b) pouring said molten metal into means for producing a plurality of spaced apart molten streams;

(c) subjecting said molten streams to an air-water jet,

said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium,

[shot] particles;

(e) air drying said [shot] particles and screening said ducing a plurality of spaced-apart molten streams;

(c) subjecting said molten streams to an air jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(f) oxidizing cadmium in said [shot] particles;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles;

(i) and cold Working said extruded [shot] particles to final shape.

3. The method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized;

(-b) pouring said molten metal into a cast iron f nnel, said funnel having a graphite insert with a plurality of spaced apart apertures, said molten metal leaving said funnel in a plurality of spaced apart streams;

(c) subjecting said molten streams to an air-water jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(-f) oxidizing cadmium in said [shot] particles;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles;

(1) and cold working said extruded [shot] particles to final shape.

4. The method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized to a temperature of about 260 C.;

(b) pouring said molten metal into a cast iron funnel, said funnel having a graphite insert with a plurality of spaced apart apertures, said molten metal leaving said funnel in a plurality of spaced apart streams;

(c) subjecting said molten streams to an air-water jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(f) oxidizing cadmium in said [shot] particles;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles;

(i) and cold working said extruded [shot] particles :to final shape.

5'. The method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized to a temperature of about 1260 C.;

(b) pouring said molten metal into a cast iron funnel, said funnel having a graphite insert with a plurality of spaced apart apertures, said molten metal leaving said tunnel in a plurality of spaced apart streams;

(c) subjecting said molten streams to an air-water jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(if) oxidizing cadmium in said silver-cadmium [shot] particles at a temperature of about 825 C.;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles;

(i) and cold working said extruded [shot] particles to final shape.

6. The method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized to a temperature of about 1260 C.

(b) pouring said molten metal into a case iron funnel, said funnel having a graphite insert with a plurality of spaced apart apertures, said molten metal leaving said funnel in a plurality of spaced apart streams;

(c) subjecting said molten streams to an air-water jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(f) oxidizing cadmium in said [shot] particles at a temperature of about 825 C. in an oxygen-containing atmosphere for 524 hours;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles;

(h) extruding said [shot] particles; and

(i) cold working said extruded [shot] particles to final shape.

7. Tthe method of manufacturing preoxidized silvercadmium oxide materials comprising the steps of:

(a) superheating a molten metal consisting essentially of silver and cadmium to be atomized to a temperature of about 1260 C.;

(b) pouring said molten metal into a cast iron funnel, said funnel having a graphite insert with a plurality of spaced apart apertures, said molten metal leaving said funnel in a plurality of spaced apart streams;

(c) subjecting said molten streams to an air-water jet, said jet breaking up said molten metal streams into small fragments;

(d) collecting and cooling the resulting silver-cadmium [shot] particles;

(e) air drying said [shot] particles and screening said shot for size;

(f) oxidizing cadmium in said silver-cadmium [shot] particles at a temperature of about 825 C. in an oxygen-containing atmosphere for 524 hours;

(g) compacting said [shot] particles;

(h) extruding said [shot] particles at about tons/ sq. in.; and

(i) cold working said extruded [shot] particles to final shape.

8. A method of manufacturing pre-oxidized silvercadmium oxide materials comprising:

(a) atomizing molten silver-cadmium alloy to form silver-cadmium alloy particles and cooling saia particles;

(b) internally oxidizing cadmium contained in said particles;

(c) compacting and heating the oxidized particles;

(d) extruding said compacted particles to form a desired shape; and

(e) working said shape to the extent necessary to obtain desired final size.

9. A method according to claim 8 in which the compacted particles are extruded into strip.

10. A method according to claim 8 in which the compacted particles are extruded into wire.

11. A method according to claim 8 in which particles not larger than approximately inch are internally oxidized.

12. A method according to claim 8 in which particles not larger titan approximately .13 inch are internally oxidized.

13. A method according to claim 8 in which in step (a) the particles are formed by atomizing at least one liquid metal stream.

14. A method according to claim 13 in which the atomization is carried out by contacting said stream with at least one fluid under pressure.

15. A method according to claim 14 in which the fluid is a material selected from the group consisting of air and air-water mixtures.

16. A method according to claim 8 in which the heating of the oxidized particles in step (c) is carried out concurrently with the compacting operation.

17. A method according to claim 8 in which the heat- 8 UNITED STATES PATENTS 1/1939 Hewsel 29182.5 7/19'42 Boegehold 75213 7/1959' Matsukawa 75206X 12/1963 Sistare 29182.5X 7/1966 GWyan, 294205X 5/1968 Schreiner et a1 75206X 6/1957 Stumbock 75173 1/ 1963 Spooner 29420X ing of oxidized particles in step (c) is carried out after 10 BENJAMIN R. PADGETT Primary Examiner A. J. STE-INER, Assistant Examiner the oxidized particles are compacted.

References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Re 27.075 Dated Februarl 23. 1971 Invent0r($) Peter C. Murphy and'Fredrik Q. Haarbye It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 6, should be changed from "Ind.; said Haarbye assignor to P.R. Mallory & Co. Inc." to

--Ind. assignors to P.R. Mallory & Co. Inc.

In the drawings, in the lower right hand corner of each sheet,

please change "INVENTOR" to INVENTORS; and add the name Peter C. Murphybelow "Fredrik O. Haarbye". Signed and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHIER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM F'o-mso (10-69) USCOMM-DC 6O375-PBQ US GOV ERNHENT PRIN'HNG OFFICE 1969 0-355-384 

